1. Field of the Invention
The invention relates to a motor for optical systems, in particular for lens systems in endoscopes. With modern video endoscopes a camera chip and also an associated lens system are incorporated in the endoscope tip. A miniaturized motor is needed for adjustment of the focal length or the focus of the lens system.
2. Description of the Relevant Art
Classical endoscopes, as can be used for example for minimal invasive surgery, convey an image by means of rod lenses from an intra-corporal objective lens to an extra-corporal eyepiece. Owing to the rod lenses, the system the system is rigid and of limited optical quality. Modern video endoscopes use a camera chip in the endoscope tip. An endoscope of this kind is disclosed in U.S. Pat. No. 7,365,768 B1. This has a rigidly disposed lens in front of the camera chip. An adjustment of the focal length of the lens is not possible.
DE 196 18 355 C2 shows a drive adapted to be incorporated in endoscopes for adjusting the focal length of a lens system. For this, a permanent magnet is moved as a slider within a stator coil. However, owing to the large mass of the permanent magnet, the drive is slow. A relationship between the coil current and the slider position is not unequivocal and additionally necessitates a path sensor with position control.
DE 37 17 872 C2 discloses a drive with a slider and a stator for a lens system in video cameras. The slider consists of two iron sleeves which are coupled to each other by a support for accommodating the lens system. The stator has two coils and also a single annular magnet for generating the magnetic fields necessary for the movement. The complex construction of the drive can be well implemented with video cameras having lens diameters in a range of centimeters, but cannot be scaled to a size in a range of millimeters, which would be needed for endoscopic applications.
DE 199 00 788 A1 discloses a motor for a valve having a permanent magnet, a coil and a solid plunger for actuating the valve.
JP 57-076805 A discloses a motor having a permanent magnet, a coil and a solid plunger. The magnetic flux runs between an end plate of the coil and the plunger through a position dependent air gap. This results in a strong nonlinearity of the force and the displacement.